U.S. patent application number 14/237306 was filed with the patent office on 2014-06-12 for ball screw and assembling method thereof.
This patent application is currently assigned to NSK Ltd.. The applicant listed for this patent is Junji Minakuchi, Masashi Shindo. Invention is credited to Junji Minakuchi, Masashi Shindo.
Application Number | 20140157927 14/237306 |
Document ID | / |
Family ID | 47714914 |
Filed Date | 2014-06-12 |
United States Patent
Application |
20140157927 |
Kind Code |
A1 |
Shindo; Masashi ; et
al. |
June 12, 2014 |
Ball Screw and Assembling Method Thereof
Abstract
To improve workability and sealing performance of a coolant when
a plurality of nuts in a ball screw are brought into contact with
one another, the plurality of nuts being coupled to one another,
assembled to one threaded shaft and cooled by flowing the coolant
through through-holes formed in the plurality of nuts in axial
directions of the plurality of nuts. The ball screw includes
counterbores of the through-holes formed on opposing end faces of
both of adjoining nuts, and a ring-shaped sealing member inserted
thereto. The counterbores are formed such that a depth of one
counterbore is larger than a length of the sealing member, and the
a depth of the other counterbore is smaller than the length of the
sealing member, and such that circumferential positions of the
counterbores of the adjoining nuts face each other when a desired
preload is exerted.
Inventors: |
Shindo; Masashi;
(Fujisawa-shi, JP) ; Minakuchi; Junji;
(Fujisawa-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Shindo; Masashi
Minakuchi; Junji |
Fujisawa-shi
Fujisawa-shi |
|
JP
JP |
|
|
Assignee: |
NSK Ltd.
Shinagawa-ku, Tokyo
JP
|
Family ID: |
47714914 |
Appl. No.: |
14/237306 |
Filed: |
August 1, 2012 |
PCT Filed: |
August 1, 2012 |
PCT NO: |
PCT/JP2012/004899 |
371 Date: |
February 5, 2014 |
Current U.S.
Class: |
74/424.81 ;
29/428 |
Current CPC
Class: |
F16H 25/2214 20130101;
Y10T 29/49826 20150115; F16H 57/0497 20130101; F16H 25/2006
20130101; F16H 57/0412 20130101; F16H 25/2209 20130101; Y10T
74/19744 20150115 |
Class at
Publication: |
74/424.81 ;
29/428 |
International
Class: |
F16H 25/22 20060101
F16H025/22 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 17, 2011 |
JP |
2011-178579 |
Oct 26, 2011 |
JP |
2011-234942 |
Claims
1. A ball screw having a threaded shaft and a plurality of nuts
coupled to one another and assembled to the threaded shaft, the
plurality of nuts being cooled by flowing a coolant through
through-holes formed in the plurality of nuts in axial directions
of the plurality of nuts, respectively, the ball screw comprising:
counterbores of the through-holes formed on opposing end faces of
both of adjoining nuts of the plurality of nuts, respectively; and
a ring-shaped sealing member having two O-rings and inserted into
the counterbores, the two O-rings being fitted on the ring-shaped
sealing member from the outside such that the two O-rings are
located within the counterbores of the adjoining nuts,
respectively; wherein a first depth of a first counterbore of the
counterbores is larger than a total length of the sealing member,
the first counterbore being formed in one of the adjoining nuts,
wherein a second depth of a second counterbore of the counterbores
is smaller than the total length of the sealing member, the second
counterbore being formed in the other of the adjoining nuts, and
wherein circumferential positions of the first counterbore and the
second counterbore of the adjoining nuts are arranged to face each
other at positions where a desired preload is exerted.
2. An assembling method of the ball screw according to claim 1, the
assembling method comprising: a step of assembling the plurality of
nuts to the threaded shaft to bring the one of the adjoining nuts
into contact with the other of the adjoining nuts in a state where
an entirety of the sealing member is accommodated in the first
counterbore formed on the one of the adjoining nuts; and a step of
pushing the sealing member after the step of assembling, in a state
where the first counterbore and the second counterbore of the
trough-holes of the adjoining nuts face each other, from an end
part of the first counterbore formed on the one of the adjoining
nuts, the end part being opposite to a contact side between the
adjoining nuts and located at an end of a through-hole of the
through-holes, the through-hole being formed in the one of the
adjoining nuts, to press the sealing member into the second
counterbore of the other of the adjoining nuts facing the one of
the adjoining nuts.
Description
TECHNICAL FIELD
[0001] The present invention relates to a ball screw, in
particular, to a ball screw in which a plurality of nuts assembled
to one threaded shaft are coupled to one another, and the nuts are
cooled by flowing a coolant through through-holes formed in the
nuts in axial directions thereof.
BACKGROUND ART
[0002] Conventionally, in a ball screw including a threaded shaft
and a nut which is in threaded engagement with the threaded shaft
and relatively rotatable, point contact or surface contact occurs
during relative rotation. Therefore, a cooling means (heat
exchanger) is sometimes provided at the nut.
[0003] As such a cooling means, a cooling passage arranged in the
nut of the ball screw for circulating the coolant is disclosed (see
e.g., Patent Literature (hereinafter referred to as PTL) 1). The
above document also discloses a cooling technique of a nut in the
ball screw adopting a double-nut preload type. The above document
also discloses a configuration having a spacer interposed between
two nuts and an O-ring attached to a mating surface of each of the
two nuts. Then, the two nuts are cooled by flowing the coolant
through the through-holes formed in the nuts in axial directions
thereof.
CITATION LIST
[0004] Patent Literature
[0005] PTL 1: JP 2010-133556 A
SUMMARY OF INVENTION
Technical Problem
[0006] In the configuration described in the above document,
however, at the time of assembling, when the two nuts come into
contact with each other in a state where the two nuts are assembled
to one threaded shaft, the O-ring attached to the mating surface
between the two nuts has to be pressed while rotating the nuts,
because of the structure of the ball screw. Therefore, the O-ring
may be sheared, thus, the sealing performance may be degraded. On
the other hand, this disadvantage can be avoided by bringing the
two nuts into contact with each other in a state where the two nuts
are detached from the threaded shaft. This reduces the workability
and increases the assembling time.
[0007] Accordingly, the present invention has been made in view of
the above-mentioned disadvantages and it is an object of the
present invention to provide a ball screw and an assembling method
thereof, in which a plurality of nuts assembled to one threaded
shaft are coupled to one another, and the nuts are cooled by
flowing a coolant through through-holes formed in the nuts in the
axial directions thereof, the ball screw being capable of improving
the workability in bringing the plurality of nuts into contact with
one another and the coolant sealing performance.
Solution to Problem
[0008] In order to solve the aforementioned problem, according to
an aspect of the present invention, there is provided a ball screw
having a threaded shaft and a plurality of nuts coupled to one
another and assembled to the threaded shaft, the plurality of nuts
being cooled by flowing a coolant through through-holes formed in
the plurality of nuts in axial directions of the plurality of nuts,
respectively. The ball screw includes counterbores of the
through-holes formed on opposing end faces of both of adjoining
nuts of the plurality of nuts, respectively, and a ring-shaped
sealing member having two O-rings and inserted into the
counterbores, the two O-rings being fitted on the ring-shaped
sealing member from the outside such that the two O-rings are
located within the counterbores of the adjoining nuts,
respectively. A first depth of a first counterbore of the
counterbores is larger than a total length of the sealing member,
the first counterbore being formed in one of the adjoining nuts and
a second depth of a second counterbore of the counterbores is
smaller than the total length of the sealing member, the second
counterbore being formed in the other of the adjoining nuts.
Moreover, circumferential positions of the first counterbore and
the second counterbore of the adjoining nuts are arranged to face
each other at positions where a desired preload is exerted.
[0009] Additionally, in order to solve the aforementioned problem,
according to another aspect of the present invention, there is
provided an assembling method of a ball screw having a threaded
shaft and a plurality of nuts coupled to one another and assembled
to the threaded shaft, the plurality of nuts being cooled by
flowing a coolant through through-holes formed in the plurality of
nuts in axial directions of the plurality of nuts, respectively.
The assembling method includes a step of using the ball screw
according to the above aspect of the present invention, and
assembling the plurality of nuts to the threaded shaft to bring the
one of the adjoining nuts into contact with the other of the
adjoining nuts in a state where an entirety of the sealing member
is accommodated in the first counterbore formed on the one of the
adjoining nuts, and a step of pushing the sealing member after the
step of using, in a state where the first counterbore and the
second counterbore of the trough-holes of the adjoining nuts face
each other, from an end part of the first counterbore formed on the
one of the adjoining nuts, the end part being opposite to a contact
side between the adjoining nuts and located at an end of a
through-hole of the through-holes, the through-hole being formed in
the one of the adjoining nuts, to press the sealing member into the
second counterbore of the other of the adjoining nuts facing the
one of the adjoining nuts.
Advantageous Effects of Invention
[0010] According to a ball screw of an aspect of the present
invention, the counterbores of the though-holes are formed on the
opposing end faces of the adjoining nuts, and the ring-shaped
sealing member having the two O-rings is inserted into the
counterbores. The two O-rings are fitted on the ring-shaped sealing
member from the outside such that the two O-rings are located
within the counterbores of the adjoining nuts, respectively. Since
the depth of the counterbore formed on the one of the adjoining
nuts is larger than the total length of the sealing member, this
counterbore can accommodate the entirety of the sealing member.
[0011] Then, the depth of the other counterbore is smaller than the
total length of the sealing member, and the circumferential
positions of the counterbores of the adjoining nuts are arranged to
face each other at positions where the desired preload is exerted.
Therefore, the two nuts can be brought into contact with each other
in a state where the entirety of the sealing member is accommodated
in the counterbore formed on the one of the two nuts. Then, in a
state where the counterbores of the though holes of the adjoining
nuts face each other, the sealing member can be pushed from the end
part of the counterbore formed on the one of the two nuts, the end
part being opposite to the contact side between the nuts and
located at the end of through hole, so that the sealing member is
pressed into the counterbore of the other of the two nuts facing
the one of the two nuts.
[0012] At this time, since the depth of the other counterbore is
smaller than the total length of the sealing member, the sealing
member can be located at the position to link the adjoined nuts, by
pushing the sealing member up to the position where the sealing
member hits the bottom of the counterbore. Therefore, there is no
possibility of shearing of the O-ring, resulting in a degradation
of the sealing performance. In addition, the workability is
improved when the adjoining nuts are brought into contact with each
other in a state the adjoining nuts are assembled to the threaded
shaft. Additionally, it is not necessary to detach each of the nuts
from the threaded shaft. And it is possible to surely seal the
coolant to prevent the leakage between a plurality of nuts.
Therefore, the sealing performance of the coolant is improved when
the adjoining nuts are brought into contact with each other in a
state the adjoining nuts are assembled to the threaded shaft.
[0013] Additionally, an assembling method of a ball screw of an
aspect of the present invention includes the step of using the ball
screw of the above aspect of the present invention, and assembling
the plurality of nuts to the threaded shaft to bring the one of the
adjoining nuts into contact with the other of the adjoining nuts in
a state where the entirety of the sealing member is accommodated in
the counterbore formed on the one of the adjoining nuts, and the
step of pushing the sealing member after the step of using, in a
state where the counterbores of the trough-holes of the adjoining
nuts face each other, from the end part of the counterbore formed
on the one of the adjoining nuts, the end part being opposite to
the contact side between the adjoining nuts and located at the end
of the through-hole, so that the sealing member is pressed into the
counterbore of the other of the adjoining nuts facing the one of
the adjoining nuts. Therefore, it is not necessary to detach each
of the nuts from the threaded shaft. And there is no possibility of
shearing of the O-ring, resulting in a degradation of the sealing
performance, thus it is possible to surely seal the coolant to
prevent the leakage between a plurality of nuts, and the
workability and the sealing performance of the coolant is improved
when the plurality of nuts are brought into contact with one
another in a state the plurality of nuts are assembled to the
threaded shaft.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a view illustrative of an embodiment of a ball
screw according to an aspect of the present invention, and is a
view illustrative of a cross section including an axial line;
[0015] FIG. 2 is a view illustrative of an assembling method of the
ball screw of FIG. 1 (an embodiment of an assembling method of a
ball screw according to an aspect of the present invention, the
same shall apply hereinafter);
[0016] FIG. 3 is a view illustrative of the assembling method of
the ball screw of FIG. 1;
[0017] FIG. 4 is a view illustrative of the assembling method of
the ball screw of FIG. 1;
[0018] FIG. 5 is a view illustrative of a modified example of the
ball screw illustrated in FIG. 1, and is an enlarged view of a
substantial part;
[0019] FIG. 6 is a view illustrative of an assembling method of the
modified example of the ball screw of FIG. 5;
[0020] FIG. 7 is a view illustrative of the assembling method of
the modified example of the ball screw of FIG. 5;
[0021] FIG. 8 is a view illustrative of the assembling method of
the modified example of the ball screw of FIG. 5; FIG. 9 is a view
illustrative of another embodiment;
[0022] FIG. 10A is a front view illustrative of an embodiment of a
spacer used in a ball screw according to an aspect of the present
invention;
[0023] FIG. 10B is a side view illustrative of the embodiment of
the spacer used in the ball screw according to the aspect of the
present invention;
[0024] FIG. 11A is a front view illustrative of another example of
the spacer illustrated in FIG. 10 (the first modified example);
[0025] FIG. 11B is a side view illustrative of the another example
of the spacer illustrated in FIG. 10 (the first modified
example);
[0026] FIG. 12A is a front view illustrative of another example of
the spacer illustrated in FIG. 10 (the second modified example);
and
[0027] FIG. 12B is a side view illustrative of the another example
of the spacer illustrated in FIG. 10 (the second modified
example).
DESCRIPTION OF EMBODIMENTS
[0028] Hereinafter, an embodiment of the present invention will be
described with reference to the attached drawings.
[0029] As illustrated in FIG. 1, a ball screw 1 according to the
present embodiment adopts a double-nut preload type. The ball screw
1 includes a threaded shaft 10, and a first nut 21 and a second nut
22 which are in threaded engagement with the threaded shaft 10 via
a plurality of rolling elements 30. An annular ring-shaped flange
20 is formed on an end of the first nut 21.
[0030] The first nut 21 and the second nut 22 are formed in a
cylindrical shape having an internal diameter larger than the
external diameter of the threaded shaft 10. A threaded groove 20a
is formed on an inner circumferential surface of each of the nuts
21 and 22 such that the threaded groove 20a faces a threaded groove
10a spirally formed on an outer circumferential surface of the
threaded shaft 10. The plurality of rolling elements 30 are
rollable in a rolling passage 2 formed by the threaded groove 10a
and the threaded groove 20a.
[0031] A spacer 40 for preventing the relative rotation between the
first nut 21 and the second nut 22 is interposed between the first
nut 21 and the second nut 22. The spacer 40 has a ring shape
(having a two halves structure as illustrated in FIG. 10) having
the same internal diameter as those of the first nut 21 and the
second nut 22. By interposing the spacer 40 between the nuts 21 and
22, a preload is exerted on the plurality of rolling elements 30
assembled between the threaded groove 20a of each of the first nut
21 and the second nut 22 and the threaded groove 10a of the
threaded shaft 10.
[0032] Two through-holes 3 penetrating through each of the nuts 21
and 22 in the axial directions thereof are formed on an upper
position and a lower position at equal intervals in a
circumferential direction. Two communication holes 7 as vertical
holes communicating with the two through-holes 3, respectively, are
formed on an upper position and a lower position at equal
intervals. Moreover, coupling nipples 8 are mounted on the side of
the two through-holes 3 of the second nut 22, respectively. Then,
the coupling nipples 8 are connected to each other by a coupling
pipe 9, thus the through-holes 3 of each of the nuts 21 and 23 are
communicated with each other circularly as a whole, thereby
constituting a circular flow passage. Then, a circulating
apparatus, not illustrated, for circulating the coolant in the two
through-holes 3 is connected via the communication holes 7 as
vertical holes. The through-holes 3 are used as a passage of the
coolant. The circulating apparatus, the through-holes 3 and the
communication holes 7 as vertical holes constitute a cooling means
50, and the each of nuts 21 and 22 is cooled by circulating the
coolant in the circular flow passage including the through-holes
3.
[0033] In the ball screw 1, counterbores 4 and 5 of the
through-holes 3 of the two nuts 21 and 22 are coaxially formed on
the opposing end faces of the nuts 21 and 22, respectively. Then,
the ball screw 1 includes a ring-shaped (hollow cylindrical)
sealing member 6 inserted into the counterbores 4 and 5. The
external diameter of the sealing member 6 is slightly smaller than
the internal diameters of the counterbores 4 and 5. Preferably, the
facing gap in the radial direction is about 0.2 mm. Moreover,
ring-shaped grooves 6m are formed on right and left ends of the
sealing member 6, respectively. Two O-rings 60 are fitted in the
grooves 6m from the outside such that the two O-rings 60 are
located within the counterbores 4 and 5 of the nuts 21 and 22,
respectively. The counterbores 4 and 5 facing each other of the two
nuts 21 and 22 are arranged such that the circumferential positions
of the counterbores 4 and 5 face each other at positions where a
desired preload is exerted, when the spacer 40 is interposed.
[0034] Also, as to the interposed spacer 40, a through-hole 40h
having the same diameter as those of the counterbores 4 and 5 is
formed such that the through-hole 40h is located coaxially with the
counterbores 4 and 5 of the adjoining nuts 21 and 22 in the axial
direction, at the circumferential positions of the counterbores 4
and 5 facing each other when the desired preload is exerted.
[0035] For further details, the spacer 40 is provided with a pair
of divided spacers 41 and 42 defined by halved ring-shaped members
as illustrated in FIG. 10. Each of the divided spacers 41 and 42
has a key groove 40k at the center of the outer circumferential
surface. Key grooves having a same shape are also formed at
corresponding positions of the outer circumferential surfaces of
the nuts 21 and 22, although not illustrated. Therefore, the
rotation of the spacer 40 relative to the nuts 21 and 22 is
prevented, in assembling, by placing a key member over the key
grooves of both of the nuts 21 and 22, and the spacer 40. In this
situation, the circumferential position where the through-hole 40h
(two through-holes 40 in this example) is formed is between the key
groove 40k and the dividing position 40b. In the example
illustrated in FIG. 10, each through-hole 40h is formed at the
center (a position almost equidistant in circumferential direction)
between the key groove 40k and the dividing position 40b. Forming
the through-hole 40h at such a position is preferable for
preventing the formation of a thin portion in the divided spacers
41 and 42.
[0036] Then, referring back to FIG. 1, the depth D2 of the
counterbore 5 of the second nut 22 as one of the nuts 21 and 22 is
larger than the total length L of the sealing member 6 (D2>L).
Therefore, the entirety of the sealing member 6 can be accommodated
in the counterbore 5. On the other hand, the depth D1 of the
counterbore 4 formed on the first nut 21 as the other of the nuts
21 and 22 is smaller than the total length L of the sealing member
6 (D1<L). Therefore, an end of the sealing member 6 protrudes
into the second nut 22 side, even when the sealing member 6 is
inserted up to the position of hitting the bottom of the
counterbore 4.
[0037] Next, the assembling method of the ball screw 1 will be
described.
[0038] In this assembling method of the ball screw, the above ball
screw 1 is used, and the two nuts 21 and 22 are brought into
contact with each other in a state where the two nuts 21 and 22 are
assembled to the threaded shaft 10, as illustrated in FIG. 2. The
steps are as follows. First, the entirety of the sealing member 6
is accommodated in the counterbore 5 formed on the second nut 22 of
the two nuts 21 and 22, as illustrated in FIG. 2 and FIG. 3. Next,
while making the two nuts face each other and interposing the
spacer 40 therebetween in this state, any of the nuts 21 and 22 is
rotated to bring the two nuts 21 and 22 into contact with each
other, as illustrated in FIG. 4.
[0039] Then, in a state where the counterbores 4 and 5 of the
trough-holes 3 of the adjoining nuts 21 and 22 face each other as
illustrated in FIG. 4, the sealing member 6 is pushed from the end
part of the counterbore 5 formed on the second nut 22, the end part
being opposite to a contact side between the nuts 21 and 22, so
that the sealing member 6 is pressed into the counterbore 4 of the
first nut 21 facing the second nut 22, until the sealing member 6
hits the bottom of the counterbore 4. At this time, as illustrated
in FIG. 4, it becomes easy to push the sealing member 6 into the
counterbore 4 of the first nut 21 facing the sealing member 6 by
using a round bar (a pushing jig) 70 formed to have an external
diameter such that the round bar 70 can be inserted in the
through-hole 3 and can push the end part of the sealing member 6
(indicated by reference sign F in FIG. 4). Therefore, the sealing
member 6 pushed into the counterbore 4 of the first nut 21 until
the sealing member 6 hits the bottom of the counterbore 4 is
located at the position to link the adjoining nuts 21 and 22, and
its position is held by the elasticity of the two O-rings 60.
[0040] Next, the operation and the advantageous effect of the
present ball screw and the present assembling method of the ball
screw will be described.
[0041] According to the ball screw 1, the counterbores 4 and 5 of
the through-holes 3 of the adjoining nuts 21 and 22 are
respectively formed on the opposing end faces of both of the
adjoining nuts 21 and 22. The ring-shaped sealing member 6 having
the two O-rings 60 is inserted into the counterbores 4 and 5. The
two O-rings 60 are fitted on the ring-shaped sealing member 6 from
the outside such that the two O-rings 60 are located within the
counterbores 4 and 5 of the adjoining nuts 21 and 22, respectively.
The counterbores 4 and 5 are formed such that the depth D2 of the
counterbore formed on the second nut 22 as the one of the nuts is
larger than the total length L of the sealing member 6. Therefore,
the entirety of the sealing member 6 can be accommodated.
[0042] Then, the circumferential positions of the counterbores 4
and 5 of the adjoining nuts 21 and 22 are arranged to face each
other at positions where the desired preload is exerted. Therefore,
the two nuts 21 and 22 can be located at the positions where the
desired preload is exerted, by bringing the nuts 21 and 22 into
contact with each other in a state where the entirety of the
sealing member 6 is accommodated in the counterbore 5 formed on the
second nut 22 as the one of the nuts.
[0043] Then, since the counterbores 4 and 5 are formed at ends of
the through-holes 3, the sealing member 6 can be pushed in a state
where the counterbores 4 and 5 of the trough-holes 3 of the
adjoining nuts 21 and 22 face each other, from the end part of the
counterbore 5 formed on the second nut 22 as the one of the nuts,
the end part being opposite to the contact side between the nuts 21
and 22 and located at the end of the through-hole 3 formed in the
second nut 22, so that the sealing member 6 is pressed into the
counterbore 4 of the first nut 21 as the other of nuts facing the
second nut 22. Therefore, the workability is improved when the
adjoining nuts 21 and 22 are brought into contact with each other
in a state the nuts 21 and 22 are assembled to the threaded shaft
10. Additionally, there is no possibility of shearing of the
O-ring, resulting in a degradation of the sealing performance.
Additionally, the position of the sealing member 6 can be held by
the two O-rings 60. Then, it is not necessary to detach each of the
nuts 21 and 22 from the threaded shaft 10. And it is possible to
surely seal the coolant to prevent the leakage between the
plurality of nuts 22 and 22.
[0044] Additionally, in the assembling method of the ball screw 1,
the above ball screw 1 is used. The plurality of nuts 21 and 22 are
assembled to the threaded shaft 10. The second nut 22 as the one of
the adjoining nuts 21 and 22 is brought into contact with the first
nut 21 as the other of nuts adjoining the second nut 22 in a state
where the entirety of the sealing member 6 is accommodated in the
counterbore 5 formed on the second nut 22 as the one of the nuts.
Then, in a state where the counterbores 4 and 5 of the trough-holes
3 of the adjoining nuts 21 and 22 face each other, the sealing
member 6 is pushed from the end part of the counterbore 5 formed on
the second nut 22 as the one of the nuts, the end part being
opposite to a contact side between the nuts 21 and 22 and located
at the end of a through-hole 3 formed in the second nut 22, so that
the sealing member 6 is pressed into the counterbore 4 of the first
nut 21 as the other of nuts facing the second nut 22. Therefore, as
described above, it is not necessary to detach each of the nuts 21
and 22 from the threaded shaft 10. And there is no possibility of
shearing of the O-ring, resulting in a degradation of the sealing
performance. Then, it is possible to surely seal the leakage of the
coolant between the plurality of nuts 22 and 22. Additionally, the
workability and the sealing performance of the coolant are improved
when the plurality of nuts 21 and 22 are brought into contact with
each other in a state the nuts 21 and 22 are assembled to the
threaded shaft 10.
[0045] It is needless to say that the ball screw and the assembling
method of the ball screw according to the present invention are not
limited to the above embodiment, and various modifications are
applicable without departing from the spirit of the present
invention.
[0046] For example, the above embodiment is described as an example
in which, the two through-holes 3 penetrating through each of the
nuts 21 and 22 in the axial direction thereof are formed on an
upper position and a lower position at equal intervals in a
circumferential direction and the through-holes 3 of each of the
nuts 21 and 23 are communicated with each other circularly as a
whole, thereby constituting a circular flow passage. However, the
present invention is not limited thereto. For example, the number
of the though-holes 3 is not limited to two, and the through-holes
3 are not necessarily formed at equal intervals.
[0047] As a specific example, four through-holes 3 penetrating
through each of the nuts 21 and 22 in the axial direction thereof
may be formed in a circumferential direction, and the two
through-holes 3 of each of the nuts 21 and 22 are used as one set,
and two sets of circular flow passages communicating circularly as
a whole may be constituted. Additionally, three or more
through-holes 3 may be formed in the circumferential direction, and
these through-holes 3 may be communicated with one another as a
whole, thereby constituting one set of circular flow passages.
[0048] In addition, the plurality of the through-holes 3 may be
arranged at unequal intervals. In this situation, as the spacer 40
illustrated in FIG. 11, for example, it is preferable that the
through-holes 3 and the through-holes 40h formed in corresponding
thereto should be formed at positions where the through-holes 3 and
40h avoid the mounting surfaces of the ball circulation tube of
each of the nuts 21 and 22 (see the reference signs 21m as 22m
illustrated in FIG. 2) and avoid the forming of a thin portion.
That is, for a phantom line 40m (a position corresponding to the
mounting surfaces 21m and 22m of the ball circulation tube) as
illustrated in FIG. 11, it is preferable to form the two
through-holes 40h of four through-holes 40h at positions between
the key grooves 40k and the phantom line 40m, in this example.
Additionally, it is preferable that other two through-holes 40h
should be formed in the same way as the above example illustrated
in FIG. 10.
[0049] Additionally, when the two through-holes 3 are formed, the
dividing positions 40b of the pair of the divided spacers 41 and 42
may be used as forming positions for the through-holes 3, and the
through-holes 3 may be formed at the each of the dividing positions
40b. In such a configuration, the through-hole is not formed at a
thick portion (a portion between the key groove 40k and the
dividing position 40b) of each of the divided spacers 41 and 42.
Therefore, it is possible to prevent the formation of a thin
portion in the divided spacers 41 and 42. Moreover, in such a
configuration, the sealing member 6 is inserted at the dividing
position 40b of the divided spacers 41 and 42. Therefore, the
replacement of the spacer 40 becomes easier. Additionally, since
the replacement of the spacer 40 becomes easier, the adjustment of
the preload also becomes easier.
[0050] Additionally, for example, the above embodiment is described
as an example of a double-nut preload type of ball screw. However,
the present invention is not limited to a preload type. The present
invention can be applied to any type of ball screw, as far as a
plurality of nuts assembled to one threaded shaft are coupled to
one another, and the nuts are cooled by flowing the coolant through
through-holes formed in the nuts in the axial directions thereof.
Additionally, the above embodiment is described as an example in
which the two nuts are coupled to each other. However, the present
invention is not limited thereto. The present invention can be
applied to a configuration in which three or more nuts are coupled
to one another.
[0051] Additionally, the above embodiment is described as an
example in which the sealing member 6 is inserted into the
counterbore 4 up to the position where the sealing member 6 hits
the bottom of the counterbore 4, so that the sealing member 6 is
located at the position to link the adjoining nuts 21 and 22 and
its position is held by the elasticity of the two O-rings 60.
However, a fixing method of the sealing member 6 is not limited
thereto. A configuration fixing the sealing member 6 with a screw
can be adopted as illustrated in FIG. 5, which is an enlarged view
of a substantial part of a modified example.
[0052] For further details, as illustrated in FIG. 5, the example
of the sealing member 6 is further provided with a ring-shaped
groove 6n at a position closer to the O-ring 6 at the counterbore 4
side, in addition to the configuration of the above embodiment.
Then, furthermore, a female thread 64 is formed through the nut 21
at a position facing the ring-shaped groove 6n when the sealing
member 6 is located at the position where the sealing member 6 hits
the bottom of the counterbore 4, and a counterbore 66 coaxial with
the female thread 64 is formed. The axial direction position can be
restricted by tightening a sealing member fixing screw 62 into the
female thread 64 to insert the tip of the sealing member fixing
screw 62 into the groove 6n.
[0053] An assembling method of the ball screw of the modified
example further including such a configuration is illustrated in
FIG. 6 to FIG. 8. First, the entirety of the sealing member 6 is
accommodated in the counterbore 5 formed on the second nut 22 of
the two nuts 21 and 22. Next, while making the two nuts face each
other and interposing the spacer 40 therebetween in this state, any
of the nuts 21 and 22 is rotated to bring the two nuts 21 and 22
into contact with each other, as illustrated in FIG. 8.
[0054] Then, in a state where the counterbores 4 and 5 of the
trough-holes 3 of the adjoining nuts 21 and 22 face each other as
illustrated in FIG. 8, the sealing member 6 is pushed from the end
part of the counterbore 5 formed on the second nut 22, the end part
being opposite to the contact side between the nuts 21 and 22, so
that the sealing member 6 is pressed into the counterbore 4 of the
first nut 21 facing the second nut 22 until the sealing member 6
hits the bottom of the counterbore 4. At this time, similarly to
the above embodiment, it becomes easy to push the sealing member 6
into the counterbore 4 of the first nut 21 facing the second nut 22
by using a round bar (a pushing jig) 70. Then, the axial direction
position of the sealing member 6 is restricted by tightening the
sealing member fixing screw 62 into the female thread 64 to insert
the tip of the sealing member fixing screw 62 into the groove 6n at
a position facing the female thread 64.
[0055] In the configuration of the above embodiment, the position
of the sealing member 6 in the axial direction is held by only the
elasticity of the two O-rings 60. Therefore, there is a possibility
of displacement of the sealing member 6 toward the second nut 22
depending on the pressure of the coolant, when the coolant
circulates in the cooling passage from the first nut 21 to the
second nut 22. Therefore, a restriction may occur to force the
circulating the coolant to flow only from the second nut 22 to the
first nut 21, when the pressure of the circulating coolant is high.
In contrast, according to the configuration of the above modified
example, although further machining for the female thread 64 and
the ring-shaped groove 6n is necessary and the working hours
increase, since the tip of the sealing member fixing screw 62 can
be caught by the groove 6n, the fixed state of the sealing member 6
does not depend on the flowing direction of the coolant. Therefore,
the configuration of this modified example is preferable when the
pressure of the coolant is high and the flowing direction of the
coolant is desired to be bidirectional.
[0056] Next, another embodiment will be described with reference to
FIG. 9.
[0057] As illustrated in FIG. 9, this embodiment is different from
the above embodiment and the above modified examples in that a coil
spring (elastic member) 75 is arranged within a cylindrical space
defined by the counterbore 5 of the second nut 22. The coil spring
75 is arranged so as to push the end part (the right side end part
in FIG. 9) of the sealing member 6 accommodated in the two
counterbores 4 and 5 toward the counterbore 4 of the first nut 21
from the counterbore 5 of the second nut 22.
[0058] Arranging the coil spring 75 eliminates the necessity of
machining of the ring-shaped groove 6n, the female thread 64 and
the counterbore 66, and eliminates the provision of the sealing
member fixing screw 62. Additionally, the movement of the sealing
member 6 due to vibration or the pressure of the coolant is
prevented. Therefore, the inexpensive configuration of arranging
the coil spring 75 further ensures the sealing. Additionally, the
coolant can flow from either one of the two nuts 21 and 22.
REFERENCE SIGNS LIST
[0059] Reference Signs List [0060] 1 ball screw [0061] 2 rolling
passage [0062] 3 through-hole [0063] 4 counterbore [0064] 5
counterbore (accommodating counterbore) [0065] 6 sealing member
[0066] 7 communication hole [0067] 8 coupling nipple [0068] 9
coupling pipe [0069] 10 threaded shaft [0070] 20 flange [0071] 21
first nut [0072] 22 second nut [0073] 30 rolling element [0074] 40
spacer [0075] 50 cooling means [0076] 60 O-ring [0077] 62 sealing
member fixing screw [0078] 64 female thread [0079] 66 counterbore
[0080] 70 round bar (pushing jig) [0081] 75 coil spring (elastic
member)
* * * * *